1. Field of the Invention
The present invention relates to a coordinate input apparatus configured to detect a pointed position on a coordinate input region, a control method adapted to control the coordinate input apparatus, and a program adapted to perform the control method.
2. Description of the Related Art
There are coordinate input apparatuses used to input coordinates designated by pointers (for example, a dedicated inputting pen, and a finger) to control computers connected thereto and to write characters, graphics, and so on.
Hitherto, various types of touch panels have been proposed or become commercially available as the coordinate input apparatuses of this kind. The touch panels are widely used because operations of terminals, such as a personal computer, can easily be directed on the screen without using special instruments.
There are various coordinate input methods, such as a method using a resistive film and a method using an ultrasonic wave. For example, U.S. Pat. No. 4,507,557 discusses a coordinate input method using light and also discusses the following configuration. That is, a retroreflecting sheet is provided outside a coordinate input region. Illumination units configured to illuminate objects with light, and light-receiving units configured to receive light are disposed at corner ends of the coordinate input region. The angle between a shielding object, such as a finger, which shields light in the coordinate input region, and each of the light receiving units is detected by using the illumination unit and the light receiving unit. According to results of the detection, the pointed position of the shielding object is determined.
Also, Japanese Patent Application Laid-Open Nos. 2000-105671 and 2001-142642 discuss coordinate input apparatuses each of which has a retroreflecting member configured around a coordinate input region, and which detects the coordinates of a part (light-shielded part), at which retroreflected light is shielded.
Among these apparatuses, the apparatus discussed in Japanese Patent Application Laid-Open No. 2000-105671 detects a peak of the intensity of light received by the light-receiving unit, which peak appears at a position corresponding to a light-shielded part and is caused by a shielding object, by performing a computing operation, such as a differentiation, on waveforms. Thus, this apparatus detects the angle of the light-shielded part with respect to the light-receiving unit. Then, this apparatus calculates the coordinates of the shielding object according to a detection result. Also, the apparatus discussed in Japanese Patent Application Laid-Open No. 2001-142642 detects one end and the other end of a light-shielded part by comparison with a specific level pattern, and then detects the center of these coordinates.
Incidentally, the methods of calculating the coordinates of a light shielding position, which are discussed in U.S. Pat. No. 4,507,557 and Japanese Patent Application Laid-Open Nos. 2000-105671 and 2001-142642, are hereunder referred to simply as the light shielding methods.
In the coordinate input apparatus according to such a light shielding method, especially, in a case where the coordinate input region has a large size, there have been demands for facilitating a plurality of operators to contemporaneously input, thereby providing a more efficient conference. Thus, a coordinate input apparatus supporting a plurality of contemporaneous inputs has been contrived.
Japanese Patent Application Laid-Open Nos. 2002-055770 and 2003-303046, and Japanese Patent Registration No. 2896183 discuss techniques of detecting angles of a plurality of light-shielded parts by each single light-receiving sensor, calculating several input coordinate candidates from a combination of the angles detected by each of the sensors, and further detecting actual inputted coordinates from the input coordinate candidates that have resulted from a contemporaneously input of a plurality of coordinates.
For example, in a case where a two point input mode is employed, the coordinates of four points are calculated at a maximum as input coordinate candidates. Among the four points, two points, the coordinates of which are actually inputted, are determined, so that the coordinates of the two points are outputted. That is, this determination is to discriminate actual input coordinates from false input coordinates among a plurality of input coordinate candidates, and to subsequently determine final input coordinates. Hereunder, this determination is referred to as “true or false determination.”
Japanese Patent Application Laid-Open No. 2003-303046 and Japanese Patent Registration No. 2896183 discuss the following techniques as practical methods of performing this true or false determination. That is, first and second sensors are provided at both ends of one side of a conventional coordinate input region to be spaced apart by a distance sufficient to precisely calculate coordinates of a pointed position within the coordinate input region. In addition, a third sensor is provided at a position between the first and second sensors to also be spaced apart from the first and second sensors by a distance sufficient to precisely calculate coordinates of a pointed position within the coordinate input region. Also, according to angle information from the third sensor, which information differs from angle information from each of the first and second sensors, the true or false determination is made on a plurality of pieces of angle information, which are detected by the first and second sensors.
Meanwhile, a method of disposing a plurality of sensor units around a coordinate input region at predetermined intervals and causing the plurality of sensor units to observe substantially the same direction and substantially the same region has been discussed to reduce the chance of, even when a plurality of light-shielded shadows overlap, one of the shadows from being detected to be completely hidden in the other shadow. Also, a method of detecting, when a plurality of shadows overlap, a direction, in which each of the shadows is present, by observing one of end portions of each of the shadows has been discussed.
The coordinate input apparatuses according to the aforementioned light shielding methods essentially can detect four coordinate candidate points that include two real images and two virtual images, for example, in a case where two input operations are concurrently performed, regardless of the configurations of the apparatuses.
However, the methods of performing true or false determinations to determine coordinate candidate points as actual input points from four coordinate candidate points have drawbacks.
For instance, the methods discussed in Japanese Patent Application Laid-Open No. 2003-303046 and Japanese Patent Registration No. 2896183 have drawbacks in that the field of view of the third sensor is insufficient to stably perform a true or false determination, that it can be difficult due to constraints on the apparatus to install the third sensor by sufficiently securing the field of view to always perform a true or false determination without an error, and that in a case where a fourth sensor is additionally provided to supplement the field of view that the third sensor does not sufficiently assure, an operation of matching detection values obtained by the sensors is complicated.
Also, in the case of the method of reducing the chance of, even when a plurality of light-shielded shadows overlap, one of the shadows from being detected to be completely hidden in the other shadow, accuracy of the true or false determination is deteriorated when one of the sensors observes the overlap of a plurality of shadows associated with actual input points. Disturbances and various fluctuations can result in erroneous true-or-false determinations. In this case, the apparatus can detect erroneous coordinates of a position that can be difficult unlikely in normal conditions.